Key switch



Nov. 5, 196s 13.61585 3,109,341

KEY SWITCH Filed June 9, 1960 K EY SIGNAL souRcEs @l uw 2 Il l :i

United States Patent O 3,109,341 KEY SWITCH Thomas B. Gibbs, Delavan, Wis., assigner to Gibbs Manufacturing t Research Corporation, a corporation of Wisconsin Filed inne 9, 1960, Ser. No. 35,045 3 Claims. (l. SLG-423) 'Ihis application is concerned ywith a key switch :for an electronic musical instrument.

In an electronic musical instrument, as an electronic organ, the keyboard is provided with a key switch mechanism actuated by the vanious keys to effect the reproduction or generation of desired tone representing signals. Often a multiple cotnact switch arrangement is utilized, one swi-tch assembly being provided -for each key of the instrument, and corresponding contacts of each key switch assembly being engageable with appropriate bus conductors. In certain types 'of instruments, and particularly those Where the tone representing signal itself is directly switched by the key actuated switches, problems have been encountered from key noise or key clicks introduced upon engagement of the key con-tact with the bus.

4It has been proposed that the key noise could be reduced or eliminated by providing spaced conductive rubber coatings on the active sections ot the bus wires, estab- ,lishing an appreciable contact resistance. In the previous arrangement for accomplishing this, the bus wires were supported by mounting plates located between the active bus sections on which the conductive rubber covering is located, with the conductor rigidly secured to the supports at each supporting point, preventing sag of the bus conductor. This construction is particularly time consuming and diiiicult to assemble.

A principal object of the present invention is the provision of improved key switch mechanisms with conductive coating means on the contact surfaces for reduci-ng or eliminating key click eiiects.

One feature of the invention is the provision in the key switch means of an elongated bus conductor arranged for engagement by the contact member of an actuated key switch having a continuous sleeve of conductive material thereon wit-h a plurality of spaced support members -for the bus and means placing the bus under tension. Another feature is that the bus supporting plates have openings therein which slidably receive the lbus conductor which is held under tension, as by a spring.

A further feature of the invention is that the conductive coating for the key switch element has a resistance variable with the pressure of the contact and several times greater upon initial contact of the switch contact member and bus than with complete actuation of the key switch.

Still another featureis that each key switch assembly has a plurality off contact members with the contact surfaces thereof coated with a resistive material. Yet a further feature i-s that the multiple contacts have terminal ends projecting Afrom a mounting block, in alignment, and an insulating plate with areas of resistive material thereon and having connect-ion portions along one side, receiving the terminal ends of the key contacts, connecting each of them with one of the resistive areas.

Further 'features and advantages of the invention will readily be apparent from the following speciiication and from the drawings, in which:

FGURE l is a simplilied block diagram illustrating the basic elements `of an electronic musical instrument pertinent to the present invention;

FIGURE 2 is a fragmentary plan view of a keyboard and key switch embodying the invention;

FIGURE 3 is a section taken generally along Iline 3 3 of FIGURE 2; and

"ice

FIGURE 4 is a reduced elevation of a modified key y switch construction.

Key noise or clicks are a problem in many types of electronic musical instruments, but are particularly troublesome in those -systems where the tone representing signals are controlled directly through the key switch, as contrasted with keying a control signal or the flike. Even thou-gh the tone handling circuitry generally includes a substantial =fixed resistance lconnected in series with the key switch, transients linitiated upon contact in the switch and noise resulting from the contact, and often accentuated by dirty switch surfaces, are objectionable.

FIGURE l illustrates, in block form, certain basic elements of an electronic musical instrument including sources 10 of tone representing signal, which may comprise a series of control oscillators and frequency dividers, key .switches 11 which may be actuated to select the desired signal or combination of signals from Sources 1t) and to connect them with suitable tone modifying iilters 12 to provide signals which accurately represent the tones to be produced. The outputs of filters 1-2 may be coupled to an amplifier 13 and reproducer or loudspeaker 14. The particular harmonics utilized and the nature of the iilters 12 may be determined by selector or stop switches (not shown).

4In FIGURE 2, a portion of the keyboard `of an electronic organ is illustrated having manually operable keys 16, which actuate associated key switch assemblies 17. With particular reference to FIGURE 3, each key switch assembly 17 includes a support or terminal block member 1S, of an insulating material, carried by a plate 19. A plurality of key switch elements or wires 20 are mounted at one end in the terminal block 18 and have contact portions Ziia 4which extend outwardly therefrom, in vertical alignment. An insulating spacer and actuator member 21 is mounted on the switch wires 2i), adjacent the contact portions 20a thereof, holding the switch elements in lixed relation to each other.

A plurality of bus conductors 22, are provided one for each switch element 2% of the switch assemblies 17. The bus conductors y22 run the length of the keyboard and are supported by a plurality of members 23 spaced along the length thereof. Each of the keys 16 has a portion 15a which extends lor projects below the lower end or" actuator member 21 and upon depression of key 16 the end portion 16a pivots upwardly lifting actuator 21 and bringing the end portion 20a of each of the switch elements 20 into contact with the associated bus conductor 22. Further details of the general construction of the keyboard may be found in Gibbs et al. application Serial No. 829,285, tiled `uly 24, 1959, now Patent No. 3,068,334, and assigned to the assignee of this invention.

The bus conductors 22 each inclu-de a conductor Wire 22a covered by a continuous sleeve 22h off a conductive, low Iresistance material. The bus conductors 22 are carried in aligned openings 24 in the support members 23, the openings being slightly smaller than the outer diameter of the covering 2Zb so that the bus conductors are held in a fixed position, but may 'be pulled through the open-ings by the application of a small amount of force. One end of the conductor 22 is fixed, as by securing wire 22a to a terminal block 25. The opposite end of the bus conductor Z2 is `connected with a lixed support 26 by a spring 27 which places the entire bus conductor under tension, holding it tight and eliminating sag between the supports 23. The tension force supplied by spring 27 is greater than the restraining frictional force on the bus conductor 22 from the supports 23.

The bus conductors may easily be assembled by merely threading them through the supports 23, securing the conductor at one end with termi-nal board 25 and attachling tension spring 27. There is no rigid physical connection between the bus conductor and the i-ndividual supports The covering ZZb on the bus conductors '22 is preferably a rubber material with particules of carbon therein providing a relatively low contact resistance between the individual switch elements 20 and the conductor 22a. 'The resistance theswitch varies with the pressure applied between the contact portions 20a of the switch elements and the `conductor and is preferably several times `eater upon initial contact than with the key elements fully raised. For example, the initial contact resistance may be of the order of 10,000 ohms and drop to =l,00 ohms upon full depression of the key. The end portions a of the switch elements ane preferably plated, as with gold, to reduce corrosion. Furthermore, the flakes ott carbon in the rubber coating of the bus conductors have a slight abrasive action which tends to clean thetips of the contact wir-esas they wipe across the bus when actuated.

A modified form of lthe invention is illustrated in FIG- URE 4. Wires, whi-oh may be gold plated, and the tip portions 31 of the individual switch elements 32, are coated with a conductive material, 3-3, as rubber with graphite flakes. This arrangement reduces the quantity of graphite containing rubber required in the instrument.

The switch assembly is preferably preassembled, with the switch elements 32. being mounte-d with the terminal or support block 33 and the spacer-actuator 34. The aligned end portions 31 of the switch members are then dipped in aliquid rubber material containing the desired proportion of graphite flakes; and the coating cured.

n In a system where .series resistors are connected with the key contacts, it is convenient and desirable to utilize printed resistors. An insulating plate 35, which may be of a ceramic material, has resistors 36 formed thereon by suitable printing process. Along the edges of plate 35 are a series of openings 37 to which circuit connections may be made. The term-inal ends 32a of the switch elements extend from mounting block 33, generally in vertical alignment and have hooked end portions B2b formed therein which are received in the 'openings 37 in plate 35 and suitably secured thereto, as by soldering. The aligned relationship of the terminal end portions 32a of the switch elements and the use of the printed resistor plate 35 facilitate assembly 0i the circuit, eliminating a great deal of handconnection and soldering which would otherwise be required. Further circuit connections may be made to similar openings or the opposite edge of plate 35. 'The dipped coatings 33 on the key switch elements are preferably much thinner than the covering 22h of bus wires of FIGURES 2 and 3, and the resistance introduced is somewhat less. In a specific system, the coatings may have a resistance of the order off 50 to 200 ohms and the series Vresistors 36 are preferably of the order of 100,000 oms. Thus a substantial variation-in the value of the resistance in the switch tip coating is permissible.

While I have shown and described certain embodiments of my invention, it is to Vbe understood that it is capable of many modiications. Changes therefore, in the construction and arrangement may be made without departing Here, the bus conductors are merely bare aroaeal fi from the spirit and scope of the invention as disclosed in the appended claims.

I claim: I y 1. in an electrical musical instrument having a plurality of linearly arranged selectively actuatable playing keys with individual con-tact members movable by individual ones of said keys, a bus bar extending linearly in a position to be engaged transversely by any off said contact membens upon the actuation of appropriate keys, said bus bar comprising a long, thin, flexible wire, and mounting means for said wire including resilient means connected to at least one end of the wire to apply a tensional Vforce to said wire suiicient to hold said Wire substantially raight and for preventing appreciable lateral displacement of said wire when said wire is transversely'engaged by one or more of said contact members.

2. In an electrical musical instrument having a plurality of linearly arranged selectively actuatable playing keys with individual Contact members movable by individual ones of said keys, a bus bar extending linearly in a position to be engaged transversely by any of said contact members upon the actuation of appropriate keys, said bus bar comprising a long, thin, iiexible wire, mounting means lor said wire including resilient means connected to at least one end of the wire to apply a tensional force to said wire sufficient to hold said wire substantially straight and for preventing appreciable lateral displacement of said wire when said wire is transversely engagedfby one or coating thereon formed of an electrically conductive elastomer.

3. In an electrical musical instlument having a plurality et linearly arranged selectively actuatable playing keys with individual contact members mo'vable by individual ones of said keys, a bus bar extending linearly in a position to be engaged transversely by any of said contact members upon the actuation of appropriate keys, said Ibus bar comprising a long, thin, exible wire, mounting means for said wire including resilient means connected to at least one end of the wire to apply a tensional force to.

said Wire suiiicient to hold `said wire substantially straight and ifor preventing appreciable lateral displacement of Y said wire when said wire is transversely engaged by one or more of said contact members, and a plurality of spaced intermediate support members -for said Wire, said intermediate support members having aligned apertures therethrough forming a loose lit with sa-id wire and throughV which said wire is threaded. f

References Cited in the le of this patent UNITED STATES PATENTS 1,248,621 Cooper Dec. 4, 1917 '2,381,309 Powell Aug. 7, 1945 2,575,230 Mork Nov. 13, 1951 2,848,920 Lester Aug. 26, 1958 2,931,877 Henley Apr. 5, r1960 2,941,433 McKellip June 2l, 1960 2,959,693 Meyer Nov. 8, 1960 FOREIGN PATENTS 807,883 Great Britain January 1959 

1. IN AN ELECTRICAL MUSICAL INSTRUMENT HAVING A PLURALITY OF LINEARLY ARRANGED SELECTIVELY ACTUATABLE PLAYING KEYS WITH INDIVIDUAL CONTACT MEMBERS MOVABLE BY INDIVIDUAL ONES OF SAID KEYS, A BUS BAR EXTENDING LINEARLY IN A POSITION TO BE ENGAGED TRANSVERSELY BY ANY OF SAID CONTACT MEMBERS UPON THE ACTUATION OF APPROPRIATE KEYS, SAID BUS BAR COMPRISING A LONG, THIN, FLEXIBLE WIRE, AND MOUNTING MEANS FOR SAID WIRE INCLUDING RESILIENT MEANS CONNECTED TO AT LEAST ONE END OF THE WIRE TO APPLY A TENSIONAL FORCE TO SAID WIRE SUFFICIENT TO HOLD SAID WIRE SUBSTANTIALLY STRAIGHT AND FOR PREVENTING APPRECIABLE LATERAL DISPLACE- 